// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
#define UI_ACCESSIBILITY_AX_TREE_UPDATE_H_

#include <stddef.h>
#include <stdint.h>

#include <string>
#include <vector>

#include "base/containers/hash_tables.h"
#include "base/strings/string_number_conversions.h"
#include "ui/accessibility/ax_node_data.h"
#include "ui/accessibility/ax_tree_data.h"

namespace ui {

// An AXTreeUpdate is a serialized representation of an atomic change
// to an AXTree. The sender and receiver must be in sync; the update
// is only meant to bring the tree from a specific previous state into
// its next state. Trying to apply it to the wrong tree should immediately
// die with a fatal assertion.
//
// An AXTreeUpdate consists of an optional node id to clear (meaning
// that all of that node's children and their descendants are deleted),
// followed by an ordered vector of zero or more AXNodeData structures to
// be applied to the tree in order. An update may also include an optional
// update to the AXTreeData structure that applies to the tree as a whole.
//
// Suppose that the next AXNodeData to be applied is |node|. The following
// invariants must hold:
// 1. Either |node.id| is already in the tree, or else the tree is empty,
//        |node| is the new root of the tree, and
//        |node.role| == WebAXRoleRootWebArea.
// 2. Every child id in |node.child_ids| must either be already a child
//        of this node, or a new id not previously in the tree. It is not
//        allowed to "reparent" a child to this node without first removing
//        that child from its previous parent.
// 3. When a new id appears in |node.child_ids|, the tree should create a
//        new uninitialized placeholder node for it immediately. That
//        placeholder must be updated within the same AXTreeUpdate, otherwise
//        it's a fatal error. This guarantees the tree is always complete
//        before or after an AXTreeUpdate.
template <typename AXNodeData, typename AXTreeData>
struct AXTreeUpdateBase {
    AXTreeUpdateBase();
    ~AXTreeUpdateBase();

    // If |has_tree_data| is true, the value of |tree_data| should be used
    // to update the tree data, otherwise it should be ignored.
    bool has_tree_data;
    AXTreeData tree_data;

    // The id of a node to clear, before applying any updates,
    // or 0 if no nodes should be cleared. Clearing a node means deleting
    // all of its children and their descendants, but leaving that node in
    // the tree. It's an error to clear a node but not subsequently update it
    // as part of the tree update.
    int node_id_to_clear;

    // A vector of nodes to update, according to the rules above.
    std::vector<AXNodeData> nodes;

    // Return a multi-line indented string representation, for logging.
    std::string ToString() const;

    // TODO(dmazzoni): location changes
};

typedef AXTreeUpdateBase<AXNodeData, AXTreeData> AXTreeUpdate;

template <typename AXNodeData, typename AXTreeData>
AXTreeUpdateBase<AXNodeData, AXTreeData>::AXTreeUpdateBase()
    : has_tree_data(false)
    , node_id_to_clear(0)
{
}

template <typename AXNodeData, typename AXTreeData>
AXTreeUpdateBase<AXNodeData, AXTreeData>::~AXTreeUpdateBase()
{
}

template <typename AXNodeData, typename AXTreeData>
std::string AXTreeUpdateBase<AXNodeData, AXTreeData>::ToString() const
{
    std::string result;

    if (has_tree_data) {
        result += "AXTreeUpdate tree data:" + tree_data.ToString();
    }

    if (node_id_to_clear != 0) {
        result += "AXTreeUpdate: clear node " + base::IntToString(node_id_to_clear) + "\n";
    }

    // The challenge here is that we want to indent the nodes being updated
    // so that parent/child relationships are clear, but we don't have access
    // to the rest of the tree for context, so we have to try to show the
    // relative indentation of child nodes in this update relative to their
    // parents.
    base::hash_map<int32_t, int> id_to_indentation;
    for (size_t i = 0; i < nodes.size(); ++i) {
        int indent = id_to_indentation[nodes[i].id];
        result += std::string(2 * indent, ' ');
        result += nodes[i].ToString() + "\n";
        for (size_t j = 0; j < nodes[i].child_ids.size(); ++j)
            id_to_indentation[nodes[i].child_ids[j]] = indent + 1;
    }

    return result;
}

} // namespace ui

#endif // UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
